The design and testing of a cam timing delay mechanism for high performance combustion engines

The performance of a high speed combustion engine can be improved by changing the cam shaft timing relative to the crank shaft timing as a function of the engine speed. In general, the camshaft should be retarded as the engine speed increases. The purpose of this investigation was to design and test a mechanical cam-retarding mechanism which would meet as many of the desired specifications as possible. Utilizing the computer to solve the response for various geometries, a conceptual design was developed and analyzed. Several types of springs were analyzed to select the stiffest, effective spring within the working stress which the space underneath the timing cover could accomodate. Stiff springs were required to decrease the torque sensitivity of the device. Consequently, high spring stresses limited the life of the proposed design. After the best physical geometry to minimize the torque dependency of the mechanism and the most effective spring had been determined, individual parts were designed. The cam retarder prototype, built to operate at lower than design speeds because of limited test facilities, was tested by employing a dynamometer to drive the test engine. The experimental results of cam speed versus relative cam rotation matched those of the analytical study once the cam torque had been determined. It was discovered that the cam torque decreased to approximately one-third of its static value as the engine speed increased. The possibility of fitting the cam retarding mechanism underneath the stock timing cover of a Chevrolet engine was found to be unrealistic.